JVM/Concurrency/MySQL/Java/Network/Redis/Linux, etc. are not all over. Would you like to squeeze BAT?
I read a post two days ago about a friend who is learning Java. All the way until Zha Shuo graduated last year. In fact, to be honest, it is true to start learning Java after graduation. At present, I also went to major companies to vote for resume interviews, but the results are quite miserable... Tencent (on one side), Meituan (on two sides), Netease Yanxuan (oc), Hangzhou byte lark (oral offer), Ali new retail business Platform (oc), Didi Trading Platform (HR side) … After reading the interview experience of these guys, I wrote this article and summarized some of the high-frequency danger points of BAT interviews (with their corresponding counterparts). The interview and study notes) are all that we must master, otherwise the interview will be bombed to death... After all, these are not "finished", and you want to go to a big factory. Is it difficult?
Advance statement: This article summarizes and analyzes the knowledge points of JVM, Redis, concurrency, MySQL, Java, network, Linux, etc., which are necessary for squeezing into BAT, and analyzes and highlights some high-frequency points, and also summarizes the corresponding points. All interviews + study notes can be shared for free, click [BAT] to get.
No nonsense, let's talk about JVM interview related
1. [Frequency] Java memory area : program counter, virtual machine stack, local method stack, heap, method area, meta space, etc. Each area must be able to introduce
2. Minor GC trigger condition: whether the remaining memory in eden area is sufficient , The two cases are analyzed separately.
3. FULL GC trigger condition: Minor GC average promotion space size> continuous remaining space in the old age, then FULL GC will be triggered
. 4. [High frequency] Methods for judging object death : reference counting method, reachability analysis algorithm (Go deeper: What are the GC root objects? Why did you choose them as GC root objects?)
5. Garbage collection algorithms: mark removal algorithm, mark sorting algorithm, copy algorithm, generational collection algorithm (in depth: advantages and applications of each algorithm Scenario)
6. Garbage collector: serial, parallel, CMS, G1, CMS, G1 focus, introduce workflow and advantages and disadvantages
7. Memory leak
- Example: {singleton, container, etc.}
- Reason: Long life cycle holds short life cycle references
8. Reference type: strong reference, soft reference, weak reference, phantom reference
9. [Frequency] Class loading process : loading, connection, initialization, what class loaders are there? Can I customize the class loader of Java.Object.String?
10. [Frequency] Introduction & Function of Parental Delegation Mechanism
PDF of notes to learn about JVM related standing: memory structure, garbage collection, class loading and bytecode technology, memory model, JVM interview questions answers, JVM tuning aspects, etc. (PDF shown in the figure below).
The second one is Java related
1. The difference between ArrayList and LinkedList
2. Comparison of HashMap & ConcurrentHashMap: thread safety issues and so on (a bit deeper: Why is HashMap thread insecure? Can you give an example = {Concurrent resize() triggers a closed loop structure and covers put operations})
3. [Frequency] HashMap related issues
- The HashMap series needs to be understood through the key source code, which is more important
- Why is the size of HashMap a power of 2?
- Can the HashMap resize() process be introduced?
- How is the efficiency of HashMap affected (load factor, hash array size)?
- What is the role of disturbance function in HashMap?
4. The difference between Hashtable and HashMap
- The underlying data structure (different after JDK1.8)
- Different parent
- Different expansion methods
- Different thread lock range (emphasis)
5. The difference between equals and ==
- Why rewrite equals to rewrite hashCode()
- The hash value is equal, and the two objects are not necessarily equals
6. [Frequency] String StringBuffer StringBuilder difference and their respective usage scenarios (in-depth: How does String realize its immutability? Why set String as an immutable object?)
7. Interface and abstract class difference
8. Rewrite and rewrite The difference between loading
9. The difference between deep copy and shallow copy
10. Three Java features
11. Object methods: finalize, clone, getClass, equals, hashCode
12. [High frequency] Design pattern: {Singleton mode, Factory mode, Decoration Maker mode, agent mode, strategy mode, etc.}
Go deeper: Why does the singleton mode use the dual detection mechanism? Why is singleton decorated with Volatile? What is the difference between decoration mode and agency mode?
Java-related notes, the most important thing is from the basic-intermediate development-senior programmer interview essential knowledge points and interview questions, as well as 23 design patterns.
The third is concurrency
1. Thread status: {new, runnalbe, wait, time-wait, block, terminated}
2. The meaning and difference of process, thread and coroutine (personal understanding is a set of progressively proposed concepts)
3. Communication between processes : Pipe, FIFO, semaphore, shared memory, message queue, Socket
4. How to avoid deadlock? The four necessary conditions for deadlock 5.
The difference between sleep and wait
6. [high frequency] the difference between Sychronized and lock?
7. Sychronized low-level optimization: no locks, biased locks, lightweight locks, heavyweight locks
8. The role of volatile: instruction retakes, ensuring the visibility of variables (design JMM)
9. ThreadLocal underlying principles
10. [High frequency 】 Thread Pool
- What parameters are involved in the thread pool constructor: {corePoolSize, maximumPoolSzie, timeout, timeUnit, RejectHandler, waiting queue, thread factory}
- Shao thread pool work process?
- What are the thread pool rejection strategies?
- What are the disadvantages of using Executor to create a thread pool?
11. AQS framework principle and source code understanding
In terms of concurrent programming, a few days ago, I got 4 points handwritten by a big cow: concurrent programming, patterns, applications, principles, and a real interview question and answer.
The fourth is MySQL (very important)
1. [High Frequency] The difference between MyISAM and InnoDB:
- Whether to support row lock
- Whether to support fifteen
- Whether to support MVCC
- The underlying index structure is different
2. Transaction characteristics ACID (a little deeper: Why is there consistency? Does AID already guarantee consistency?)
3. Problems caused by concurrent transactions: dirty reads, loss of modifications, non-repeatable reads, phantom reads
4. [ High frequency] Transaction isolation level
5. [High frequency] MVCC mechanism
6. [High frequency] Index
- Why the index uses B+ tree structure instead of B tree
- Why does the index use B+ tree structure instead of red-black tree: Disk pre-read, red-black tree height
7. What is the difference between a clustered index and a non-clustered index? Do you understand primary key indexes and secondary indexes?
8. Why not create an index for each column?
9. [Frequency] SQL statement optimization, SQL topic (byte requirement code)
10. What is the meaning of the rows type key extra field in explain?
11.count(1) count(*) count (column value) difference
MySQL is really very important. There are a lot of things in this area. What kind of tuning, interviews, learning PDFs, and many thieves. These PDFs are all essential learning books in the following figure.
Redis is also indispensable (Meituan has a soft spot for Redis)
1. Why use redis / why use cache (high performance, high concurrency)
2. Why use redis instead of map/guava for caching?
3. Redis common data structure and usage scenario analysis ( String, Hash, List, Set) , Sorted Set )
4. Redis set expiration time
5. Redis memory elimination mechanism ( There are 2000w data in MySQL, and only 20w data in Redis. How to ensure that the data in Redis is hot data? )
6. Redis persistence mechanism ( How to ensure that the data can be restored after redis is hung up and restarted )
7. Common Redis exceptions and solutions ( cache penetration, cache avalanche, cache warm-up, cache degradation )
8. Common application scenarios in distributed environments ( distributed locks) , Distributed self-incrementing ID )
9. Redis cluster mode ( master-slave mode, sentinel mode, Cluster cluster mode )
10. How to solve the concurrent competition of Redis Key problem
11. How to ensure the data consistency of the cache and database double write?
Redis answers have been sorted out as follows
Network aspect
1. TCP/IP model & OSI model
2. Application layer, transport layer, network layer common protocols: DNS, HTTP, FTP, STMP, SSL, TCP, UDP, ARP, IP
3. [High frequency] TCP three-way handshake, TCP Wave four times
- Go deeper: Why can we shake hands twice?
- What is the time_wait state with four waves? close-wait state?
- In what scenarios is the time_wait state too much, and what problems will it cause?
4. TCP reliability: ARQ, flow control, congestion control, checksum
5. [Frequency] The process of entering URL to display the homepage // I have only encountered it once, but I feel a lot of questions after seeing it.
6. HTTPS and HTTP difference (a little deeper: introduction to the HTTPS encryption process?)
7. The difference between Cookie and Session
8. The difference between Http1.0 and HTTP1.1 and Http2.x
9. The difference between get and post
10. Common status codes
The network part stayed up a few days ago and compiled the following 5 interview knowledge points, which have detailed answers
About the operating system (relatively less)
1. The difference between user mode and kernel mode
2. Fork() function
3. Select poll epoll difference
4. Virtual memory function? The role of memory paging?
5. Introduction of page fault exception
6. Difference between OOM problem and StackOverFlow
other
1. Need to understand linux instructions
Regarding linux commands, you can actually look at this "Linux. Command Collection" which is sorted by installation purpose (26 alphabetical order)
2. Need to understand some big data scenarios. For example, 100 million data is top 10, 100 million data is top 10, and 100 million URLs are repeated URLs.
3.64 horses and 8 tracks. How many races are the top eight? Waiting for intellectual questions (byte often test)
……
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BAT-close at hand, far away, everyone wants to "squeeze". Big factories are dreams. If you want to turn your dreams into reality, you have to rely on yourself. If you can't stop even Redis, JVM, concurrency, MySQL, Java, and the Internet, how about BAT?
The article summarizes and analyzes some of the knowledge points you must have before interviewing BAT such as JVM, concurrency, MySQL, Java, network, Redis, Linux , etc., and there are also corresponding notes PDF** (the editor has been organized into However, in fact, these are just a few of them, and there are many others that I won’t introduce one by one. Interested friends can share them for free) **, it is essential for preparing for an interview or studying. Please give me a thumbs up, [click here] to download all these PDFs (interview + study) for free.